Help with standard deviation=/

Skromnaya · 2010-02-21 09:35:13

i did get 2606.1

bobbym · 2010-02-21 09:37:08

Hi;

OK, now divide that 2606.1 by 9 and then take the square root of that.

Skromnaya · 2010-02-21 09:40:22

so it's 289.57 and the square root of that is 17.016

bobbym · 2010-02-21 09:45:24

That is very good. Remember you do what is inside the square root first just like a parentheses. Also that formula is for the standard deviation of a sample not the entire population. Since your data is the population and not a sample from a population the formula you are using is not correct. But don't tell your teacher, keep using what he/she tells to use. OK?

LQ · 2010-02-21 09:48:20

I understand that the sum is what was difficult. Just square every value together with the mean value but negative. then you divide probably with as many squares it was minus one. After that you draw the square root out of the whole shabang. Correct me if I'm wrong bobbym.

Skromnaya · 2010-02-21 09:52:34

STUPID ME!!!!!I just realized we need to find the standard deviation for the sample population=(((9

bobbym · 2010-02-21 09:56:09

Hi LQ;

No your not wrong. just a little off here.

Just square every value together with the mean value but negative

Think of it as squaring every value after you have subtracted the mean from it.

Rest is OK.

LQ · 2010-02-21 09:56:35

I suppose that's the equation that bobbym left at page one? refering to second last post.

Last edited by LQ (2010-02-21 09:57:46)

Skromnaya · 2010-02-21 09:57:47

so the answer that i got can also be the answer for the sample population?

LQ · 2010-02-21 10:00:16

w8 hold on. ehm. what it is it is ever is and that's the entire population, as to say, there must be an equation for it, thought that was on last page? Let me check... Yes, post 13. Questions?

Last edited by LQ (2010-02-21 10:01:17)

Skromnaya · 2010-02-21 10:02:07

But i haven't learned that formula in class=/

bobbym · 2010-02-21 10:03:04

Hi Skromnaya;

That formula is for the sample from a population. If that is the population you use 10 instead of 9. Personally I like what we did and wouldn't change it.

LQ · 2010-02-21 10:07:57

To make short; squares/amount of them. squares contain samples and minused means. squareroot all, so solves samples

Last edited by LQ (2010-02-21 10:14:34)

Skromnaya · 2010-02-21 10:09:36

oh ok thanksss soooooo much=)can you help me with one last question?It deals with the same problem.
The question is:
A dietitian obtains the amounts of sugar (in centigrams) from 100 centigrams in each of 10 different cereals, including Cheerios, Corn Flakes, Fruit Loops, Trix, and 7 others. Those values are listed below.Is the standard deviation of these values likely to be a good estimate of the standard deviation of the amounts of sugar in each gram of cereal consumed by the population of all Americans who eat cereal?Why or why not?

3,24,30,47,43,7,47,13,44,39

LQ · 2010-02-21 10:23:08

squareroot(((3-20)^2 + (24-20)^2 + (30-20)^2 + (47-20)^2 + (43-20)^2 + (7-20)^2 + (47-20)^2 + (13-20)^2 + (44-20)^2 + (39-20)^2))/10)

So many numbers, so many misstakes one can make D: but that looks correct so far, correct me if I'm wrong. Can you calculate it from there?

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